Is there a link between agricultural irrigation and earthquakes?

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Scientists noticed an increased occurrence of earthquakes in southern Monterey County, close to Parkfield, California. Stumped as to why, Colin B. Amos, assistant professor of geology at Western Washington University, and his team set-out to find an answer.

Just a few days ago, their report was released with a possible reason: the pumping of groundwater in the Central Valley. Since the mid-1800s, groundwater has been pumped to irrigate the surrounding farms and cities.

Today, the Central Valley produces one-quarter of the United States’ food, including 40% of its fruits and nuts. It’s the second-most-pumped aquifer system in the nation. Amos’ report suggests that the earth, no longer pinned down by the heavy groundwater, uplifts, resulting in small earthquakes.

Does this mean humans are responsible for these earthquakes? Has the pumping of massive amounts of groundwater over the past 150 years, disturbed the earth’s upper crust? Could little quakes influence bigger quakes in Los Angeles or San Francisco? Or, could little quakes release tension on the San Andreas fault, leading to a lesser possibility of the Big One?

Guests:

Bill Hammond, Research Professor at the Nevada Geodetic Laboratory, Nevada Bureau of Mines and Geology; Co-Author of the study

Tom Holzer, research geologist with the Earthquake Hazards Team of U.S. Geological Survey